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1. Seeing the Disturbed Forest for the Trees: Remote Sensing Is Underutilized to Quantify Critical Zone Response to Unprecedented Disturbance

   https://doi.org/10.1029/2022EF003314  

   Hwang, Kyotaek ; Harpold, Adrian A. ; Tague, Christina L. ; Lowman, Lauren ; Boisramé, Gabrielle F. S. ; Lininger, Katherine B. ; Sullivan, Pamela L. ; Manning, Aidan ; Graup, Louis ; Litvak, Marcy ; et al ( July 2023 , Earth's Future)

   Understanding the severity and extent of near surface critical zone (CZ) disturbances and their ecosystem response is a pressing concern in the face of increasing human and natural disturbances. Predicting disturbance severity and recovery in a changing climate requires comprehensive understanding of ecosystem feedbacks among vegetation and the surrounding environment, including climate, hydrology, geomorphology, and biogeochemistry. Field surveys and satellite remote sensing have limited ability to effectively capture the spatial and temporal variability of disturbance and CZ properties. Technological advances in remote sensing using new sensors and new platforms have improved observations of changes in vegetation canopy structure and productivity; however, integrating measures of forest disturbance from various sensing platforms is complex. By connecting the potential for remote sensing technologies to observe different CZ disturbance vectors, we show that lower severity disturbance and slower vegetation recovery are more difficult to quantify. Case studies in montane forests from the western United States highlight new opportunities, including evaluating post‐disturbance forest recovery at multiple scales, shedding light on understory vegetation regrowth, detecting specific physiological responses, and refining ecohydrological modeling. Learning from regional CZ disturbance case studies, we propose future directions to synthesize fragmented findings with (a) new data analysis using new or existing sensors, (b) data fusion across multiple sensors and platforms, (c) increasing the value of ground‐based observations, (d) disturbance modeling, and (e) synthesis to improve understanding of disturbance.

    

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2. Wildfire alters the disturbance impacts of an emerging forest disease via changes to host occurrence and demographic structure

   https://doi.org/10.1111/1365-2745.13495  

   Simler‐Williamson, Allison B. ; Metz, Margaret R. ; Frangioso, Kerri M. ; Rizzo, David M. ; Thrall, ed., Peter ( September 2020 , Journal of Ecology)

   Anthropogenic activities have altered historical disturbance regimes, and understanding the mechanisms by which these shifting perturbations interact is essential to predicting where they may erode ecosystem resilience. Emerging infectious plant diseases, caused by human translocation of nonnative pathogens, can generate ecologically damaging forms of novel biotic disturbance. Further, abiotic disturbances, such as wildfire, may influence the severity and extent of disease‐related perturbations via their effects on the occurrence of hosts, pathogens and microclimates; however, these interactions have rarely been examined.

   The disease ‘sudden oak death’ (SOD), associated with the introduced pathogenPhytophthora ramorum, causes acute, landscape‐scale tree mortality in California's fire‐prone coastal forests. Here, we examined interactions between wildfire and the biotic disturbance impacts of this emerging infectious disease. Leveraging long‐term datasets that describe wildfire occurrence andP. ramorumdynamics across the Big Sur region, we modelled the influence of recent and historical fires on epidemiological parameters, including pathogen presence, infestation intensity, reinvasion, and host mortality.

   Past wildfire altered disease dynamics and reduced SOD‐related mortality, indicating a negative interaction between these abiotic and biotic disturbances. Frequently burned forests were less likely to be invaded byP. ramorum, had lower incidence of host infection, and exhibited decreased disease‐related biotic disturbance, which was associated with reduced occurrence and density of epidemiologically significant hosts. Following a recent wildfire, survival of mature bay laurel, a key sporulating host, was the primary driver ofP. ramoruminfestation and reinvasion, but younger, rapidly regenerating host vegetation capable of sporulation did not measurably influence disease dynamics. Notably, the effect ofP. ramoruminfection on host mortality was reduced in recently burned areas, indicating that the loss of tall, mature host canopies may temporarily dampen pathogen transmission and ‘release’ susceptible species from significant inoculum pressure.

   Synthesis. Cumulatively, our findings indicate that fire history has contributed to heterogeneous patterns of biotic disturbance and disease‐related decline across this landscape, via changes to the both the occurrence of available hosts and the demography of epidemiologically important host populations. These results highlight that human‐altered abiotic disturbances may play a foundational role in structuring infectious disease dynamics, contributing to future outbreak emergence and driving biotic disturbance regimes.

    

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3. Long‐term responses to large‐scale disturbances: spatiotemporal variation in gastropod populations and communities

   https://doi.org/10.1111/oik.09605  

   Presley, Steven J. ; Willig, Michael R. ( July 2023 , Oikos)

   The Anthropocene is characterized by complex, primarily human‐generated, disturbance regimes that include combinations of long‐term press (e.g. climate change, pollution) and episodic pulse (e.g. cyclonic storms, floods, wildfires, land use change) disturbances. Within any regime, disturbances occur at multiple spatial and temporal scales, creating complex and varied interactions that influence spatiotemporal dynamics in the abundance, distribution and biodiversity of organisms. Moreover, responses to disturbance are context dependent, with the legacies of previous disturbances affecting responses to ensuing perturbations. We use three decades of annual data to evaluate the effects of repeated pulse disturbances and global warming on gastropod populations and communities in Puerto Rico at multiple spatial scales. More specifically, we quantify 1) the relative importance of large‐scale and small‐scale aspects of disturbance on variation in abundance, biodiversity and species composition; and 2) the spatial scales at which populations and communities integrate information in the spatially heterogenous environments created by disturbances. Gastropods do not exhibit consistent decreases in abundance or biodiversity in association with global warming: abundance for many species has increased over time and species richness does not evince a temporal trend. Nonetheless, gastropods are sensitive to hurricane severity, spatial environmental variation and successional trajectories of the flora. In addition, they exhibit context dependent (i.e. legacy effects) responses that are scale dependent. The Puerto Rican biota has evolved in a disturbance‐mediated system. This historical exposure to repeated, severe hurricane‐induced disturbances has imbued the biota with high resistance and resilience to the current disturbance regime, resulting in an ability to persist or thrive under current environmental conditions. Nonetheless, these ecosystems may yet be threatened by worsening direct and indirect effects of climate change. In particular, more frequent and severe hurricanes may prevent the establishment of closed canopy forests, negatively impacting populations and communities that rely on these habitats.

    

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4. Compound disease and wildfire disturbances alter opportunities for seedling regeneration in resprouter‐dominated forests

   https://doi.org/10.1002/ecs2.2991  

   Simler‐Williamson, Allison B. ; Metz, Margaret R. ; Frangioso, Kerri M. ; Meentemeyer, Ross K. ; Rizzo, David M. ( December 2019 , Ecosphere)

   Human‐altered disturbance regimes and changing climatic conditions can reduce seed availability and suitable microsites, limiting seedling regeneration in recovering forest systems. Thus, resprouting plants, which can persist in situ, are expected to expand in dominance in many disturbance‐prone forests. However, resprouters may also be challenged by changing regimes, and the mechanisms determining facultative seedling recruitment by resprouting species, which will determine both the future spread and current persistence of these populations, are poorly understood. In the resprouter‐dominated forests of coastal California, interactions between wildfire and an emerging disease, sudden oak death (SOD), alter disturbance severity and tree mortality, which may shift forest regeneration trajectories. We examine this set of compound disturbances to (1) assess the influence of seed limitation, biotic competition, and abiotic conditions on seedling regeneration in resprouting populations; (2) investigate whether disease‐fire interactions alter postfire seedling regeneration, which have implications for future disease dynamics and shifts in forest composition. Following a wildfire that impacted a preexisting plot network in SOD‐affected forests, we monitored seedling abundances and survival over eight years. With pre‐ and postfire data, we assessed relationships between regeneration dynamics and disturbance severity, biotic, and abiotic variables, using Bayesian generalized linear models and mixed models. Our results indicate that postfire seedling regeneration by resprouting species was shaped by contrasting mechanisms reflecting seed limitation and competitive release. Seedling abundances declined with decreasing postfire survival of mature, conspecific stems, while belowground survival of resprouting genets had no effect. However, where seed sources persisted, seedling abundances and survival generally increased with the prefire severity of disease impacts, suggesting that decreased competition with adults may enhance seedling recruitment in this resprouter‐dominated system. Species’ regeneration responses varied with their relative susceptibility to SOD and suggest compositional shifts, which will determine future disease management and forest restoration actions. These results additionally highlight that mechanisms related to biotic competition, seed limitation, and opportunities for seedling recruitment beneath mature canopies may determine possible shifts in the occurrence of resprouting traits. This result has broad applications to other systems impacted by human‐altered regimes where asexual persistence may be predicted to be a beneficial life history strategy.

    

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5. Wildfire impacts on root‐associated fungi and predicted plant–soil feedbacks in the boreal forest: Research progress and recommendations

   https://doi.org/10.1111/1365-2435.14205  

   Hewitt, Rebecca E. ; Day, Nicola J. ; DeVan, M. Rae ; Taylor, D. Lee ( October 2022 , Functional Ecology)

   Root-associated fungi play a critical role in plant ecophysiology, growth and subsequent responses to disturbances, so they are thought to be particularly instrumental in shaping vegetation dynamics after fire in the boreal forest. Despite increasing data on the distribution of fungal taxonomic diversity through space and time in boreal ecosystems, there are knowledge gaps with respect to linking these patterns to ecosystem function and process. Here we explore what is currently known about postfire root-associated fungi in the boreal forest. We focus on wildfire impacts on mycorrhizal fungi and the relationships between plant–fungal interactions and forest recovery in an effort to explore whether postfire mycorrhizal dynamics underlie plant–soil feedbacks that may influence fire-facilitated vegetation shifts. We characterize the mechanisms by which wildfire influences root-associated fungal community assembly. We identify scenarios of postfire plant–fungal interactions that represent putative positive and negative plant–soil feedbacks that may impact successional trajectories. We highlight the need for empirical field observations and experiments to inform our ability to translate patterns of postfire root-associated fungal diversity to ecological function and application in models. We suggest that understanding postfire interactions between root-associated fungi and plants is critical to predict fire effects on vegetation patterns, ecosystem function, future landscape flammability and feedbacks to climate. 

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